The polymerization of unsaturated monomers commercially is normally conducted in large vessels or reactors which are frequently provided with auxiliary equipment, such as baffles, heat transfer coils, instrument wells, stirring or mixing means, and the like. Vinyl chloride, for example, when polymerized either alone or with other vinylidene comonomers, is normally polymerized in water in the presence of suspending, dispersing or emulsifying agents and free radical forming catalysts in pressure polymerization reactors. In such polymerizations, in both the suspension and emulsion systems, polymer is usually deposited on surfaces of the polymerization reactor walls, baffles, agitator and other exposed surfaces. This polymer build-up normally begins as a thin layer, often referred to as paper build-up, which, with successive charges, becomes increasingly heavy, of a sandy and often hard nature. These undesirable polymer deposits on the surfaces of the equipment with which the reaction mixtures come into contact interfere with the efficient heat transfer. Further, these deposits have a tendency to deteriorate. The deposits often break off of the surfaces, resulting in contamination of the reaction mixture and the products produced therefrom.
It is very often necessary, after each polymerization reaction is completed, to open the reactor amd scrape the polymer build-up off the walls, baffles and agitator, etc. An operation such as this is costly, both in labor and down-time of the reactor, i.e., lost production. In order to reduce polymer build-up, it has been proposed to coat the interior surfaces of the polymerization vessels with various materials prior to the start of the reaction. As examples of some of these coating materials, reference is made to U.S. Pat. Nos. 4,024,330, polyaromatic amines in organic solvents; 4,024,301, polyaromatic amines in aqueous alkali; 4,255,470, polyaromatic amines in HCl solution; 4,080,173, self-condensed polyhydric phenols in aqueous alkali; 4,228,130, polyhydric phenol-sodium hypochlorite reaction products; 4,105,840, aqueous solutions of tannins and tannates; 3,825,434, a first coating of a phenolic, epoxide, etc., coated with an insolubilized hydrophilic polymer; and 4,142,033, a 2 layer coating of a dye and a methocel; and the like.
These coating materials, and others, have proved to be useful in reducing, and in many cases eliminating polymer build-up, but in some cases they have contributed to polymer discoloration. Further in some applications, as in materials exposed to food or in medical applications, the presence of smaller amounts of these materials is often required, so that their efficiency is reduced. The industry requires improved method to prevent this build-up on polymerization surfaces exposed to the polymerization medium.